1. Field of the Invention
The present invention relates to methods of measuring and calibrating inclination of an electron beam in an electron beam proximity exposure apparatus, as well as an electron beam proximity exposure apparatus.
2. Description of the Related Art
An electron beam proximity exposure apparatus of this kind has conventionally been disclosed in U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent No. 2951947).
FIG. 11 shows a basic configuration of this electron beam proximity exposure apparatus. This electron beam proximity exposure apparatus 10 is composed of an electron gun 12 mainly including an electron beam source 14 which generates electron beams 15, a lens 16 which makes the electron beams 15 parallel with each other, and a shaping aperture 18; a scanning device 20 which includes main deflectors 22 and 24 and sub-deflectors 26 and 28 to cause the electron beams to scan a mask while remaining parallel with an optical axis; a mask 30; an electrostatic chuck 50; and an XY stage.
The mask 30 is arranged in proximity to a wafer 40 attracted to the electrostatic chuck 60 so that the gap between the mask 30 and the wafer 40 is, for example, 50 xcexcm. In this state, when emitted perpendicularly to the mask 30, electron beams pass through the mask pattern on the mask 30 and then fall on a resist layer 42 on the wafer.
The main deflectors 22 and 24 of the scanning device 20 controls deflection of the electron beams 15 so that the electron beams scan the entire surface of the mask 30 as shown in FIG. 12. This causes the mask pattern of the mask 30 to be transferred to the resist layer 42 on the wafer 40 on an equal scale.
Further, the sub-deflectors 26 and 28 of the scanning device 20 controls an angle at which the electron beams are incident on the mask pattern so as to correct distortion of the mask (inclination correction). Now, when the angle at which the electron beams 15 are incident on the mask 30 is defined as xcex1 and the gap between the mask 30 and the wafer 40 is defined as G as shown in FIG. 13, the amount xcex4 of deviation of a mask pattern transferred position resulting from the incident angle xcex1 is expressed by the following equation:
xcex4=Gxc2x7tan xcex1. 
In FIG. 13, the mask pattern is transferred to a position deviating from the regular one by the amount xcex4. Accordingly, if the mask 30 is distorted, for example, as shown in FIG. 14(A), the mask pattern is transferred without any distortion as shown in FIG. 14(B) by controlling the inclination of the electron beams according to the distortion of the mask observed at a position scanned by the electron beams.
The XY stage 60 moves the wafer 40 attracted to the electrostatic chuck 50, in two horizontally orthogonal axial directions. Each time the equal-scale transfer of the mask pattern is completed, the XY stage 60 moves the wafer 40 a predetermined distance to enable a plurality of mask patterns to be transferred to the single wafer 40.
If the main deflectors 22 and 24 control deflection of the electron beams 15 so that the electron beams scan the entire surface of the mask 30, then the electron beams must scan the mask while remaining parallel with the optical axis as shown in FIG. 11. Thus, the inclination of the electron beams 15 must be accurately measured according to the position scanned by the electron beams 15.
Further, if the sub-deflectors 26 and 28 control the angle at which the electron beams 15 are incident on the mask pattern, the relationship between a voltage applied to the sub-deflectors 26 and 28 and the angle at which the electron beams 15 are incident on the mask pattern must be previously determined.
The present invention is achieved in view of these points, and it is an object thereof to provide a method of measuring inclination of an electron beam in an electron beam proximity exposure apparatus, the method enabling the inclination of the electron beam to be accurately measured and enabling determination of the relationship between a voltage applied to sub-deflectors and the angle at which the electron beam is incident on a mask pattern.
It is another object of the present invention to provide a method of calibrating inclination of an electron beam in an electron beam proximity exposure apparatus as well as an electron beam proximity exposure apparatus wherein the electron beam can scan a mask while remaining parallel with an optical axis when the electron beam scans the entire surface of the mask.
To attain the above objects, the present invention is directed to a method of measuring inclination of an electron beam in an electron beam proximity exposure apparatus which transfers a mask pattern formed on a mask to a resist layer on a wafer, wherein the electron beam proximity exposure apparatus comprises: an electron gun that emits the electron beam with a predetermined sectional shape; the mask arranged in proximity to the wafer; a deflector that controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the mask; a calibration mask having a plurality of marks previously formed thereon; a first electron beam detecting device which has a first mark and which converts the electron beam passing through the first mark into an electrical quantity; a second electron beam detecting device which has a second mark located above the first mark and below the calibration mask and which converts the electron beam passing through the second mark into an electrical quantity; and a moving device which moves the first and second electron beam detecting devices on an xy plane which is orthogonal to an optical axis of the electron beam, the method comprising the steps of: (a) loading the calibration mask and using the deflector to control deflection of the electron beam so that the electron beam impinges on an arbitrary mark of the calibration mask; (b) detecting a position of the first electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through a first mark of the first electron beam detecting device to make the electrical quantity detected by the first electron beam detecting device largest; (c) detecting a position of the second electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through a second mark of the second electron beam detecting device to make the electrical quantity detected by the second electron beam detecting device largest; (d) calculating the inclination of the electron beam observed when the electron beam is deflected so as to impinge on the arbitrary mark of the calibration mask according to positions of the first electron beam detecting device in x and y directions after movement, the positions being detected in the step (b), positions of the second electron beam detecting device in the x and y directions after movement, the positions being detected in the step (c), the amounts of positional difference between the first and second marks in the x and y directions, and a difference in height between the first and second marks; and (e) repeating the steps (a) to (d) for each mark of the calibration mask to determine the inclination of the incident electron beam for each mark.
According to the present invention, at the step (b), the position of the first electron beam detecting device after movement is detected when the mark of the calibration mask and the first mark are on the electron beam axis. Similarly, at the step (c), the position of the second electron beam detecting device after movement is detected when the mark of the calibration mask and the second mark are on the electron beam axis. Accordingly, when the amounts of positional difference between the first and second marks in the x and y directions are already known or detected, the inclination of the electron beam deflected so as to impinge on the mark of the calibration mask can be calculated from geometrical relations based on the positions of the first electron beam detecting device in the x and y directions after movement, the positions of the second electron beam detecting device in the x and y directions after movement, and the difference in height between the first and second marks. Likewise, the inclination of the electron beam can be calculated when the electron beam is deflected so as to impinge on another mark of the calibration mask.
Preferably, the amounts of positional difference between the first and second marks in the x and y directions are determined by: allowing the electron beam to impinge on a mark of the calibration mask located on an optical axis of the electron gun without deflecting the electron beam using the deflector; detecting the position of the first electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through the first mark of the first electron beam detecting device to make the electrical quantity detected by the first electron beam detecting device largest; detecting the position of the second electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through the second mark of the second electron beam detecting device to make the electrical quantity detected by the second electron beam detecting device largest; and determining the amount of deviation according to the detected position of the first electron beam detecting device in the x and y directions and the detected position of the second electron beam detecting device in the x and y directions.
The present invention is also directed to method of calibrating inclination of an electron beam in an electron beam proximity exposure apparatus, the method comprising the steps of: determining an inclination correction value for each mark formed on the calibration mask, the inclination correction value being used to zero the inclination of the electron beam determined by the above-described method of measuring inclination of the electron beam in the electron beam proximity exposure apparatus; creating an inclination correction table that stores correction values correspondingly to a position scanned by the electron beam; when the deflector is used to control deflection of the electron beam emitted by the electron gun so that the electron beam scans the entire surface of the mask, reading out a corresponding inclination correction value from the inclination correction table according to the position scanned by the electron beam and controlling the deflector according to the readout inclination correction value; and calibrating the electron beam so that the electron beam is parallel with the optical axis regardless of the position scanned by the electron beam.
According to the present invention, with the above-described method of measuring inclination of the electron beam, the inclination of the electron beam can be measured for each of the plurality of marks of the calibration mask (that is, the inclination according to the position scanned by the electron beam on the mask) when the electron beam passes through the mark. When the entire surface of the mask is scanned to expose the mask pattern to the electron beam to thereby transfer the pattern to the wafer, located in proximity to the mask pattern, the inclination of the electron beam is calibrated according to the correction table, which stores inclination correction values used to zero the inclination of the electron beam correspondingly to the position scanned thereby, so that the electron beam is parallel with the optical axis regardless of the position scanned thereby.
The present invention is also directed to a method of calibrating inclination of an electron beam in an electron beam proximity exposure apparatus which transfers a mask pattern formed on a mask to a resist layer on a wafer, wherein the electron beam proximity exposure apparatus comprises: an electron gun that emits the electron beam with a predetermined sectional shape; the mask arranged in proximity to the wafer; a main deflector which controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the mask; a sub-deflector which controls the inclination of the electron beam impinging on the mask; an electron beam detecting device which has two marks arranged on an axis which is parallel with an optical axis of the electron gun, the marks being located at different heights, the electron beam detecting device converting the electron beam passing through the two marks into an electrical quantity; and a moving device which moves the electron beam detecting device to an arbitrary position scanned by the electron beam, the method comprising the steps of: (a) moving the electron beam detecting device to the arbitrary position scanned by the electron beam and using the main deflector to deflect the electron beam so that the electron beam impinges on the electron beam detecting device; (b) varying the inclination of the electron beam using a voltage applied to the sub-deflector and detecting the voltage applied when the electrical quantity detected by the electron beam detecting device is largest; (c) executing the steps (a) and (b) by varying the position of the electron beam detecting device and creating a correction table that stores the voltage applied to the sub-defector correspondingly to the position scanned by the electron beam; and (d) when the main deflector is used to control deflection of the electron beam emitted by the electron gun so that the electron beam scans the entire surface of the mask, reading out a corresponding voltage from the inclination correction table according to the position scanned by the electron beam, and applying the voltage to the sub-deflector, wherein calibration is executed so that the electron beam is parallel with the optical axis regardless of the position scanned by the electron beam.
According to the present invention, using the sub-deflector which can control the inclination of the electron beam entering the mask when the main deflector controls deflection of the electron beam so that the electron beam scans the entire surface of the mask, the inclination of the electron beam is calibrated so as to make the electron beam parallel with the optical axis regardless of the position scanned by the electron beam. The voltage applied to the sub-deflector at the time of calibrating the inclination of the electron beam corresponds to the one applied to the sub-deflector when the electrical quantity detected by the electron beam detecting means is largest (that is, when the electron beam is orthogonal to the mask surface) and stored in the correction table according to the position scanned by the electron beam and the stored voltage is used.
The present invention is also directed to a method of measuring inclination of an electron beam in an electron beam proximity exposure apparatus which transfers a mask pattern formed on a mask to a resist layer on a wafer, wherein the electron beam proximity exposure apparatus comprises: an electron gun that emits the electron beam with a predetermined sectional shape; the mask arranged in proximity to the wafer; a main deflector which controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the mask; a sub-deflector which controls the inclination of the electron beam impinging on the mask; a calibration mask having a plurality of marks previously formed thereon; a first electron beam detecting device which has a first mark and which converts the electron beam passing through the first mark into an electrical quantity; a second electron beam detecting device which has a second mark located above the first mark and below the calibration mask and which converts the electron beam passing through the second mark into an electrical quantity; and a moving device which moves the first and second electron beam detecting devices on an xy plane which is orthogonal to an optical axis of the electron beam, the method comprising the steps of: (a) loading the calibration mask and using the main deflector to control deflection of the electron beam so that the electron beam impinges on an arbitrary mark of the calibration mask; (b) applying a predetermined voltage to the sub-deflector to incline the electron beam; (c) detecting a position of the first electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through the first mark of the first electron beam detecting device to make the electrical quantity detected by the first electron beam detecting device largest; (d) detecting a position of the second electron beam detecting device after movement when the electron beam, having passed through the mark of the calibration mask, passes through the second mark of the second electron beam detecting device to make the electrical quantity detected by the second electron beam detecting device largest; (e) using the main deflector to deflect the electron beam so that the electron beam impinges on the arbitrary mark of the calibration mask, according to positions of the first electron beam detecting device in x and y directions after movement, the positions being detected in the step (c), positions of the second electron beam detecting device in the x and y directions after movement, the positions being detected in the step (d), and the amounts of positional difference between the first and second marks in the x and y directions, and calculating at least one of the inclination of the electron beam and the amount of deflection thereof observed when a predetermined voltage is applied to the sub-deflector; and (f) repeating the steps (a) to (d) for each mark of the calibration mask to determine for each mark relationship between the voltage applied to the sub-deflector and the at least one of the inclination of the electron beam and the amount of deflection thereof associated with the voltage.
According to the present invention, the inclination of electron beam incident on the mark of the calibration mask or the amount of deflection thereof is calculated when the predetermined voltage is applied to the sub-deflector. The inclination of the electron beam or the amount of deflection thereof is measured using a method similar to the above-described method. Likewise, the inclination of electron beam deflected so as to enter another mark of the calibration mask or the amount of deflection thereof is calculated when the predetermined voltage is applied to the sub-deflector. This enables, for each mark of the calibration mask (that is, for each scanned position on the mask), determination of the relationship between the voltage applied to the sub-deflector and the inclination of the electron beam or the amount of deflection thereof associated with this voltage. The thus determined relationship between the voltage applied to the sub-deflector and the inclination of the electron beam or the amount of deflection thereof is used to control deflection of the electron beam so that the electron beam has a desired inclination or deflection amount at an arbitrary scanned position on the mask.
The present invention is also directed to an electron beam proximity exposure apparatus which transfers a mask pattern formed on a transfer mask to a resist layer on a wafer, the electron beam proximity exposure apparatus comprising: an electron gun that emits an electron beam with a predetermined sectional shape; the transfer mask arranged in proximity to the wafer; a main deflector which controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the transfer mask; a sub-deflector which controls inclination of the electron beam impinging on the transfer mask; a correction table which stores information indicating, for each mark of the calibration mask measured by the above-described method of measuring inclination of the electron beam, relationship between a voltage applied to the sub-deflector and the at least one of the inclination of the electron beam and the amount of deflection thereof associated with the voltage; a distortion table which stores information on distortion of the transfer mask; and a control device which controls, when the wafer is exposed to the electron beam, the voltage applied to the sub-deflector according to the information stored in the correction and distortion tables, a value for a gap between the wafer and the transfer mask, and a position on the transfer mask scanned by the electron beam, in order to correct the distortion of the transfer mask.
According to the present invention, even if the transfer mask is distorted, the mask pattern can be transferred by exposure to the wafer as precisely as in the case with an undistorted mask.
The present invention is also directed to an electron beam proximity exposure apparatus which transfers a mask pattern formed on a transfer mask to a resist layer on a wafer, the electron beam proximity exposure apparatus comprising: an electron gun that emits an electron beam with a predetermined sectional shape; the transfer mask arranged in proximity to the wafer; a main deflector which controls deflection of the electron beam emitted by the electron gun so that the electron beam scans an entire surface of the transfer mask; a sub-deflector which controls inclination of the electron beam impinging on the transfer mask; a correction table which stores information indicating, for each mark of the calibration mask measured by the above-described method of measuring inclination of the electron beam, relationship between a voltage applied to the sub-deflector and the at least one of the inclination of electron beam and the amount of deflection thereof associated with the voltage; a setting device having expansion and contraction rates of a current wafer in x and y directions set relatively to a same wafer during a predetermined process; and a control device which controls, when the wafer is exposed to the electron beam, the voltage applied to the sub-deflector according to the information stored in the correction table, the expansion and contraction rates of the wafer in the x and y directions set by the setting device, a value for a gap between the wafer and the transfer mask, and a position on the transfer mask scanned by the electron beam, in order to vary a transfer scale in the x and y directions in proportion to the expansion and contraction rates of the wafer in the x and y directions.
According to the present invention, even if expansion or contraction of the wafer varies the ratio of the size of the mask pattern of the mask to the size of the mask pattern transferred to the wafer, the transfer scale can be precisely corrected so that the mask patterns transferred by exposure to the wafer will not locationally deviate from each other.